This invention relates to turbochargers and control devices therefor. More specifically, this invention relates to an improved pressure-responsive actuator for controlling the operation of a turbocharger.
Turbochargers are well known in the prior art, and typically comprise a trubine for driving a compressor to supply relatively high pressure charge air to a combustion engine. The turbine is rotatably driven by exhaust gases from the engine, and in turn rotatably drives a compressor for compressing intake air supplied to the engine. One major design problem with turbochargers, however, is that the rotational speed of the turbine and the compressor increases as the speed and/or load of the engine increases. At relatively high operating speeds or loads, it is possible for the turbine and compressor to be driven at speeds above critical design limits, or for the compressor to supply charge air to the engine at boost pressures higher than the engine can withstand.
A wide variety of control devices for turbochargers has been developed to limit the rotational speed of the turbocharger compressor, and thereby control the level of boost supplied by the compressor. Such devices may be blow-off or pop-off valves, turbine wastegate valves, compressor inlet control valves, and the like. These valve devices are generally similar to each other in principle in that each comprises a valve responsive to a predetermined pressure level or pressure differential to restrict the availability of gases for driving the turbine, or for compression by the compressor. For example, a turbine wastegate valve operates within a passage bypassing the turbine, and when opened by a pressure responsive valve actuator, allows a portion of the engine exhaust gases to bypass the turbine to atmosphere. In this manner, the turbine is rotatably driven by a relatively reduced mass flow of exhaust gases to limit the rotational speed of the turbine, and thereby also limit the rotational speed and resultant boost pressure of the compressor.
Pressure responsive valve actuators typically comprise an actuator housing including a diaphragm dividing the housing into a pair of separated chambers. Inlet ports are provided for coupling the two chambers to a different sources of pressure to subject the diaphragm to a predetermined pressure differential. Changes in the pressure differential, such as may occur during increase or decrease in engine speed of load, cause displacement of the diaphragm which in turn displaces an actuator rod connected to the diaphragm. The rod projects out of the housing, and is connected to an appropriate valve structure on the compressor or turbine for positioning the valve to control turbocharger operation.
In practice, one major consideration in the design of pressure responsive valve actuators is to provide an adequate seal allowing passage of the actuator rod housing without significant gas leakage. This is particularly important wherein the pressure sources coupled to the actuator housing comprise gaseous air-fuel mixtures, and wherein the actuator housing is mounted close to hot engine components or the turbine of the turbocharger. In this regard, prior art seals which satisfactorily prevent gas leakage have restricted movement of the actuator rod to axial movement only. This type of seal finds its primary application wherein the actuator rod comprises a valve stem connected directly to or formed integrally with a valve head, and wherein axial rod movement is sufficient to properly position the valve head. See, for example, U.S. Pat. Nos. 3,035,408; 3,091,077; 3,104,520; 3,195,805; 3,196,606; 3,270,495; 3,389,553; 4,005,578; 4,005,579 and 4,019,323; all of which relate to valve actuators with axially movable valve stems or rods. However, it is sometimes desirable to use other types of valve structures, such as relatively inexpensive butterfly valve or the like positionally adjusted by movement of a crank arm. With these valve structures, at least some arcuate motion of the actuator rod is required for adjusting the position of the valve. However, with prior art devices wherein the actuator rod is constrained for axial movement, relatively complex and multiple link mechanical couplings have been required between the rod and the valve structure for providing the desired arcuate movement. See, for example, U.S. Pat. Nos. 2,356,124; 2,374,708 and 3,069,614.
The present invention overcomes the problems and disadvantages of the prior art by providing an improved actuator for controlling the operation of a turbocharger having an outwardly projecting actuator rod, and means for sealing the housing to allow for axial and angular movement of the actuator rod with respect to the housing.